Start by cutting up a whole onion into thin slices and slicing the beef very finely.
Add 80ml of tsuyu and 80ml of water to a frying pan and turn on the heat.
After a few moments, add the onion to the pan and allow it to cook for a minute or two, or until the onions are soft.
Add the sliced beef to the pan and cook on full heat until the beef is fully cooked.
Fill up two bowls with cooked rice about half-way and then add the cooked beef and onions on top. You can pour some of the liquid over also for extra flavour if you like.
Garnish the dish with beni shoga pickled red ginger and shichimi chilli powder before serving.
It is popular in Japan to crack a raw egg over a freshly made bowl of gyudon. If that sounds a bit intense, try adding an egg or two to the pan after the beef is done and cook for a few minutes extra.